1. Field of the Invention
This invention is in the field of launch vehicle/spacecraft isolation systems, and in particular, relates to a combined active/passive system to isolate a spacecraft from its launch vehicle.
2. Description of the Prior Art
It has been shown that the launch environment is the worst loading condition that a satellite will ever see during its lifetime. Since launch environments account for much of the expense in designing, qualifying, and testing spacecraft components, significant costs can be saved if these loads are reduced. Also, with today's promise of lighter and cheaper satellites, reducing launch loads is a necessary step in achieving these goals. When satellites become smaller and lighter, smaller launch vehicles can be used which further reduce launch costs, but at the expense of a harsher ride to orbit compared with a larger sized launch vehicle. For a satellite to survive the launch environment, the traditional approach in the satellite design is to structurally stiffen the satellite. This is a very inefficient way to design satellites considering the fact that a kg of mass costs thousands of dollars to put into space. Also, since the total spacecraft weight is restricted, increasing bus structural or instrument weight to survive the launch environments will significantly decrease the mission of the satellite.
Another approach for the satellite to survive the launch environment is to reduce the dynamics to auxiliary components by incorporation of passive damping or local isolation. However, these approaches are spacecraft-specific and invariably add time and cost to the spacecraft development. A whole-spacecraft isolator, on the other hand, can reduce launch environments to the whole satellite and can be tunable for any shape or size of satellite. Once the launch loads are reduced, the satellite can be designed to these lower loads which will save satellite mass.
The Boeing Company's Launch Vibration Isolation System (LVIS) was an all-active whole-spacecraft isolation system for the larger launch vehicles such as their Delta-II. LVIS concept had significant drawbacks since it used hydraulics and air springs, which tend to leak over a period of time. This becomes extremely significant when the system has to sit on a launch pad up to weeks in advance of the launch.